Mechanisms of manganese transport in rabbit erythroid cells.

Abstract

1. The mechanisms of manganese transport into erythroid cells were investigated using rabbit reticulocytes and mature erythrocytes and 54Mn‐labelled MnCl2 and Mn2‐transferrin. In some experiments iron uptake was also studied. 2. Three saturable manganese transport mechanisms were identified, two for Mn2+ (high and low affinity processes) and one for transferrin‐bound manganese (Mn‐Tf). 3. High affinity Mn2+ transport occurred in reticulocytes but not erythrocytes, was active only in low ionic strength media such as isotonic sucrose and had a Km of 0.4 microM. It was inhibited by metabolic inhibitors and several metal ions. 4. Low affinity Mn2+ transport occurred in erythrocytes as well as in reticulocytes and had Km values of approximately 20 and 50 microM for the two types of cells, respectively. The rate of Mn2+ transport was maximal in isotonic KCl, RbCl or CsCl, and was inhibited by NaCl and by amiloride, valinomycin, diethylstilboestrol and other ion transport inhibitors. The direction of Mn2+ transport was reversible, resulting in Mn2+ efflux from the cells. 5. The uptake of transferrin‐bound manganese occurred only with reticulocytes and depended on receptor‐mediated endocytosis of Mn‐Tf. 6. The characteristics of the three saturable manganese transport mechanisms were similar to corresponding mechanisms of iron uptake by erythroid cells, suggesting that the two metals are transported by the same mechanisms. 7. It is proposed that high affinity manganese transport is a surface representation of the process responsible for the transport of manganese across the endosomal membrane after its release from transferrin. Low affinity transport probably occurs by the previously described Na(+)‐Mg2+ antiport, and may function in the regulation of intracellular manganese concentration by exporting manganese from the cells.

Transport mechanisms for iron and other transition metals in rat and rabbit erythroid cells

“…The inhibition of iron and manganese transport into reticulocytes by some of the metals studied in the present work has been reported previously (Morgan, 1988;Chua et al 1996). This inhibition was investigated systematically and more completely in the present work by determining the effect of varying concentrations of unlabelled metals on the uptake of radiolabelled samples of the metals by reticulocytes when the cells were incubated in sucrose solution with 1 ìÒ concentrations of the labelled metals or in KCl solution with 20 ìÒ concentrations.…”

“…The incubation procedure was essentially the same as described earlier (Chua et al 1996). Usually, samples of the cell suspensions (usually 100 ìl) were incubated in an oscillating, temperaturecontrolled water bath in 2 ml of the incubation solutions containing radiolabelled divalent sulphate (Fe, Co) or chloride (Mn, Ni, Zn, Cd) salts of the metals.…”

“…Based on the results of previous investigations on the transport of non-transferrin-bound iron (Morgan, 1988;Quail & Morgan, 1994;Hodgson, Quail & Morgan, 1995) and manganese (Chua et al 1996) into rabbit erythroid cells, three basic incubation media were chosen for the present studies, viz. isotonic NaCl, KCl and sucrose.…”

“…A range of biochemical reagents have been shown to inhibit Fe¥ and Mn¥ uptake by reticulocytes Chua et al 1996). In the present work these reagents were tested for their effects on the uptake of the other metals by reticulocytes, as well as on Fe¥ and Mn¥ uptake.…”

Pharmacokinetics of pulmonary manganese absorption: evidence for increased susceptibility to manganese loading in iron-deficient rats

“…Thus the major difference in the partitioning of the two isotopes between plasma and cellular fractions of blood in iron-deficient rats suggests that unique pathways for manganese uptake and/or retention may exist. For example, in addition to the uptake of transferrin-bound manganese, high-and low-affinity transport of Mn(II) by reticulocytes and erythrocytes has been reported (10).…”